Introduction

AEROCE

Transport in the MBL

Synoptic scale transport

Intercontinental transport

Model studies of O₃ sources

Anthropogenic influences,
central N. Atlantic

PICO-NARE

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of the International Global Atmospheric Chemistry Project G

A Note from the IGAC Chair: Guy Brasseur Towards a Second Phase of IGAC When IGAC was created in the late 1980’s, clear scientific objectives were established with the purpose of solving important issues related to global atmospheric chemistry and global change. At that time, very little information on the global budgets of chemical species was available, and the global distribution of key compounds in the troposphere was virtually unknown. The photochemical theory for the lower atmosphere, especially in remote environments, had not been tested in situ, and chemical transport models were in their infancy. In fact, most of the efforts by the scientific community in the 1980’s had focused primarily on issues related to stratospheric ozone; time had come to investigate how changes in the chemical composition of the troposphere would affect the Earth system. The importance of biosphere/atmosphere interactions was soon identified as a priority for the Project, and the role of aerosols became another important IGAC focus. Several field experiments were organized under the IGAC umbrella in various parts of the world, with superb results published in different special issues of professional journals. The two most recent experiments endorsed by IGAC are ACE-Asia (supported by NSF in the United States as well as agencies in several Asian countries) and TRACE-P (supported by NASA), both in the western Pacific and with a strong international participation. The major success of IGAC is probably that a large international scientific community with focus on global atmospheric chemistry has been formed and has become very active. International scientific conferences sponsored by IGAC (with various partners) have presented exciting results on several occasions. A synthesis of many efforts conducted by this community is nearing completion and will appear in a few months in a volume prepared by a large group of experts. It has been reviewed extensively and can be considered as a first international assessment on global tropospheric chemistry. This integration/synthesis document is a major milestone in IGAC history, and it will conclude the first phase of the Project. Time has therefore come to start defining the scientific objectives and an organizational structure for a new phase of IGAC. This second phase is expected to begin in , 2003. A “transition team” to guide preparation of the new phase of IGAC is being formed now and will be co-chaired by Mary Scholes (South Africa) and Tim Bates (United States). Both are world-class scientists who have contributed very substantially to IGAC’s science. The task of the transition team will be to establish new priorities for research in atmospheric chemistry on the regional to global scale. Issues like upper troposphere/lower stratosphere processes, long-range transport of pollutants, multiphase chemistry, cloud-chemistry interactions and chemistry-climate couplings are examples of topics that the new IGAC will have to consider. A workshop will be held in Sweden late this year or early in 2002 to develop scientific themes and priorities for the next 10 years. Because of the breadth of the new themes for IGAC in the future, it is hoped that, in addition to IGBP and CACGP, the two parent organizations of IGAC, stronger links will be established with other related programs, in particular the World Climate Research Programme (WCRP) and its SPARC Project.